A Space Hulk is the term given by the Imperium of Man to the wreckage of a starship or a mangled twist of various starships and artificial debris found drifting through the vacuum of the Milky Way Galaxy without apparent direction. Many times they are so huge that they have their own atmosphere and gravity. Since the Hulks often exit and re-enter the Warp seemingly at random, searching or traveling within them is dangerous in the extreme. Space Hulks have many times been used as a means of transport by certain unsophisticated factions. The Orks, the Genestealers, and even Chaos Space Marine renegades use them occasionally to invade other worlds. As the Warp jump of Space Hulks is essentially made in a random direction, this gives them the advantage of surprise over Imperial or Eldar forces. These monstrosities often drop in and out of the Warp, threatening to carry Chaos Space Marines, Orks or Genestealers that have entered stasis who can launch attacks upon the unsuspecting planets of the Imperium. The Imperial Navy, and all Imperial forces and authorities as a whole, have standard orders to survey such objects and to report their location. The Hulks often consist of starships and items of technology millennia old, and the recoverable technology can be of immense value to the Imperium, and especially to the Adeptus Mechanicus. Thus elite Imperial forces are sent aboard to clear out infestations. Depending on the strategic situation (availability of troops, proximity to vital Imperial star systems, safety margins, etc.) Space Marines are usually sent to purge the Hulk of any alien or Chaotic infestations. The reason for this intense interest is that Space Hulks have been adrift in the void often for hundreds or even thousands of years, forming an unrecognizable huge mass, in which technological and scientific bounties from the Dark Age of Technology could be stowed that would be of great commercial value.

Many Space Hulks are known to be breeding grounds for the Tyranid species known to the Imperium as the Genestealers, often being the product of a starship inflicted with a Genestealer infestation where the Genestealers took over and killed the crew. It is even suspected by the Adeptus Mechanicus' Magos that the Tyranid Hive Mind implants Genestealers to lay in stasis on Space Hulks to serve as unwitting living vanguards for a nearby Tyranid Hive Fleet intent on finding new worlds to consume. Congruent with the expansive bio-mass consumption of the Tyranids, these Genestealer-infested Space Hulks are doubly dangerous for the cargo they may contain and the Hive Fleets they could psychically call upon an inhabited planet.

As a result of the dangers, the mission of boarding and exploring Space Hulks is normally entrusted to Terminators, a Space Marine Chapter's most experienced elite warriors who are heavily armed and armoured. In some cases this is an impossible task, due to powerful enemy resistance, too few available Imperial troops, the Space Hulk being too close to vital Imperial star systems, etc. In such cases the bombardment and total destruction of the Hulk is the only viable alternative. However, Space Hulks are huge and durable, and even Nova Cannon blasts are not powerful enough to take one down.

Cauldron Born - The Cauldron Born is a former Space Hulk and the current fortress-ship and home of the Renegade Blood GorgonsChapter of Chaos Space Marines. The Cauldron Born is an artefact of Blood Gorgons biological experimentation, including the use of pseudo-surgery and daemonology. It is said that the hull of the floating fortress has been grafted with the flesh of a Daemon Prince and that organic matter has been cultivated to merge with the ship’s engines, spawning a Daemonic Spirit that inhabits the vessel's circuitry.

Mortis Thule - Known by many names, the Mortis Thule -- Death From Beyond the Horizon -- was the largest Space Hulk known to exist within the Jericho Reach, and was very possibly the most dangerous. Though each Hulk is unique, Mortis Thule stands out not only for its enormous size but also for its long history in the Reach, dating back to before the arrival of the Imperial Expeditionary Fleets of the Great Crusade. Most Hulks either fall apart given time (or sufficient massed firepower), or disappear back into the Warp never to be seen again. The Mortis Thule seems older than many such Space Hulks encountered before; its curious longevity and increasing mass are possibly tied to that other mysterious artefact of the Reach, the Warp Gate.

Red Polyphemus - The Red Polyphemus was a Space Hulk that appered during the Manachean War, one of the early campaigns of the Horus Heresy and that diverted much of Port Maw's strength before the attack of the Traitors on the Manachean Commonwealth in the Ultima Segmentum. It is commonly believed that this particular Space Hulk was diverted in the Warp by the will of the Chaos Gods to aid their mortal followers.

Revenant Rex - The Revenant Rex was the Space Hulk that was destroyed by the Crimson ConsulsChapter, at the cost of their entire 1st Company and the Battle BargeIncarnadine Ecliptic.

Sin of Damnation - The Sin of Damnation was the Space Hulk assaulted by the Blood Angels Space Marines in Space Hulk (the board game).